Polyvinylchloride (PVC) is a widely used plastic in industrial and consumer products. Rigid PVC is used for structural members, piece parts, pipes and tubing, etc. Semirigid PVC is widely used for flooring, siding and other building materials. Flexible PVC is used widely for fabrics, wall coverings and electrical wire insulation. Other uses are too numerous to mention.
Flexible PVC is made using a range of types and amounts of plasticizers. These materials soften the normally rigid PVC and impart the desired degree of flexibility. However, the plasticizers are rarely very soluble in PVC, and they tend to migrate out of the host material and enter the environment. This is an important consequence if the plasticizer material is environmentally unsafe or unwanted. Migration is also a problem from a cosmetic standpoint because the plasticizers commonly used absorb stains during use and migrate back into the surface of the plastic along with the staining substance where they cannot be removed conveniently but are nevertheless visible.
Among the important uses of flexible PVC mentioned earlier is wire insulation. The following description is framed in terms of this use, but it should be understood that virtually all uses for flexible PVC share common circumstances within the context of this invention. Therefore the invention is to be construed as directed toward any article of manufacture comprising plasticized PVC.
Electrical wire insulated with polyvinylchloride (PVC) is used widely for many applications and often for plug-in cords for consumer appliances. It is also used widely for cords connecting telephone station equipment with wall or floor line junctions. In these applications the cords typically have high visibility coupled with high exposure to wear, staining and environmental degradation. Black cords suffer little from staining and only moderately from degradation. However, the increasing demand for cords that are coordinated in color with appliances or interior decor places stringent demands on the PVC insulation. Staining and discoloration are significant problems, especially with equipment that receives heavy use and has a long service life. To reduce inventory necessary to provide a full range of color selection it is sometimes desirable to offer a universal cord with insulation made of clear plastic. Clear plastic insulation has been found to have more market acceptance than black or a neutral color. However, the clear plastic insulation also suffers from the problems enumerated before.
As indicated earlier, staining of light colored and clear PVC cords is often due to the plasticizer required to impart flexibility to the PVC. The stain combines with the plasticizer and migrates back into the plastic where it cannot be removed, even with abrasive type cleaners, but can still be seen.
In accordance with one aspect of this invention the problem of staining is overcome by coating the clear or colored PVC with a plasticizer barrier to prevent interaction between the plasticizer and a potential staining substance. The barrier is a coating of a polyester blend that itself is clear as applied to the cord, and which adheres well to plasticized PVC, is abrasion resistant, flexible, has long term stability against heat and light, can be processed by conventional extrusion, and is itself resistant to stains and discoloration.
While this description has centered about PVC insulated electrical cords, and in particular, telephone mounting cords, it should be understood that the coating materials described and claimed are similarly useful for any PVC product. Top coatings for vinyl upholstery and fabrics are typical of such related uses. These applications often involve the same kind of performance factors for the PVC that are enumerated above.